Putrescine analogue cytotoxicity against Trypanosoma cruzi

Putrescine Depletion in Leishmania donovani Parasites Causes Immediate Proliferation Arrest Followed by an Apoptosis-like Cell Death

The polyamine pathway in Leishmania parasites has emerged as a promising target for therapeutic intervention, yet the functions of polyamines in parasites remain largely unexplored. Ornithine decarboxylase (ODC) and spermidine synthase (SPDSYN) catalyze the sequential conversion of ornithine to putrescine and spermidine. We previously found that Leishmania donovani Δodc and Δspdsyn mutants exhibit markedly reduced growth in vitro and diminished infectivity in mice, with the effect being most pronounced in putrescine-depleted Δodc mutants. Here, we report that, in polyamine-free media, ∆odc mutants arrested proliferation and replication, while ∆spdsyn mutants showed a slow growth and replication phenotype. Starved ∆odc parasites also exhibited a marked reduction in metabolism, which was not observed in the starved ∆spdsyn cells. In contrast, both mutants displayed mitochondrial membrane hyperpolarization. Hallmarks of apoptosis, specifically DNA fragmentation and membrane modifications, were observed in Δodc mutants incubated in polyamine-free media. These results show that putrescine depletion had an immediate detrimental effect on cell growth, replication, and mitochondrial metabolism and caused an apoptosis-like death phenotype. Our findings establish ODC as the most promising therapeutic target within the polyamine biosynthetic pathway for treating leishmaniasis.

A combined ligand and target-based virtual screening strategy to repurpose drugs as putrescine uptake inhibitors with trypanocidal activity

Chagas disease, also known as American trypanosomiasis, is a neglected tropical disease caused by the protozoa Trypanosoma cruzi, affecting nearly 7 million people only in the Americas. Polyamines are essential compounds for parasite growth, survival, and differentiation. However, because trypanosomatids are auxotrophic for polyamines, they must be obtained from the host by specific transporters. In this investigation, an ensemble of QSAR classifiers able to identify polyamine analogs with trypanocidal activity was developed. Then, a multi-template homology model of the dimeric polyamine transporter of T. cruzi, TcPAT12, was created with Rosetta, and then refined by enhanced sampling molecular dynamics simulations. Using representative snapshots extracted from the trajectory, a docking model able to discriminate between active and inactive compounds was developed and validated. Both models were applied in a parallel virtual screening campaign to repurpose known drugs as anti-trypanosomal compounds inhibiting polyamine transport in T. cruzi. Montelukast, Quinestrol, Danazol, and Dutasteride were selected for in vitro testing, and all of them inhibited putrescine uptake in biochemical assays, confirming the predictive ability of the computational models. Furthermore, all the confirmed hits proved to inhibit epimastigote proliferation, and Quinestrol and Danazol were able to inhibit, in the low micromolar range, the viability of trypomastigotes and the intracellular growth of amastigotes.

The repositioned drugs disulfiram/diethyldithiocarbamate combined to benznidazole: Searching for Chagas disease selective therapy, preventing toxicity and drug resistance

Chagas disease (CD) affects at least 6 million people in 21 South American countries besides several thousand in other nations all over the world. It is estimated that at least 14,000 people die every year of CD. Since vaccines are not available, chemotherapy remains of pivotal relevance. About 30% of the treated patients cannot complete the therapy because of severe adverse reactions. Thus, the search for novel drugs is required. Here we tested the benznidazole (BZ) combination with the repositioned drug disulfiram (DSF) and its derivative diethyldithiocarbamate (DETC) upon Trypanosoma cruzi in vitro and in vivo. DETC-BZ combination was synergistic diminishing epimastigote proliferation and enhancing selective indexes up to over 10-fold. DETC was effective upon amastigotes of the BZ- partially resistant Y and the BZ-resistant Colombiana strains. The combination reduced proliferation even using low concentrations (e.g., 2.5 µM). Scanning electron microscopy revealed membrane discontinuities and cell body volume reduction. Transmission electron microscopy revealed remarkable enlargement of endoplasmic reticulum cisternae besides, dilated mitochondria with decreased electron density and disorganized kinetoplast DNA. At advanced stages, the cytoplasm vacuolation apparently impaired compartmentation. The fluorescent probe H2-DCFDA indicates the increased production of reactive oxygen species associated with enhanced lipid peroxidation in parasites incubated with DETC. The biochemical measurement indicates the downmodulation of thiol expression. DETC inhibited superoxide dismutase activity on parasites was more pronounced than in infected mice. In order to approach the DETC effects on intracellular infection, peritoneal macrophages were infected with Colombiana trypomastigotes. DETC addition diminished parasite numbers and the DETC-BZ combination was effective, despite the low concentrations used. In the murine infection, the combination significantly enhanced animal survival, decreasing parasitemia over BZ. Histopathology revealed that low doses of BZ-treated animals presented myocardial amastigote, not observed in combination-treated animals. The picrosirius collagen staining showed reduced myocardial fibrosis. Aminotransferase de aspartate, Aminotransferase de alanine, Creatine kinase, and urea plasma levels demonstrated that the combination was non-toxic. As DSF and DETC can reduce the toxicity of other drugs and resistance phenotypes, such a combination may be safe and effective.

Unique thiol metabolism in trypanosomatids: Redox homeostasis and drug resistance

Trypanosomatids are mainly responsible for heterogeneous parasitic diseases: Leishmaniasis, Sleeping sickness, and Chagas disease and control of these diseases implicates serious challenges due to the emergence of drug resistance. Redox-active biomolecules are the endogenous substances in organisms, which play important role in the regulation of redox homeostasis. The redox-active substances like glutathione, trypanothione, cysteine, cysteine persulfides, etc., and other inorganic intermediates (hydrogen peroxide, nitric oxide) are very useful as defence mechanism. In the present review, the suitability of trypanothione and other essential thiol molecules of trypanosomatids as drug targets are described in Leishmania and Trypanosoma. We have explored the role of tryparedoxin, tryparedoxin peroxidase, ascorbate peroxidase, superoxide dismutase, and glutaredoxins in the anti-oxidant mechanism and drug resistance. Up-regulation of some proteins in trypanothione metabolism helps the parasites in survival against drug pressure (sodium stibogluconate, Amphotericin B, etc.) and oxidative stress. These molecules accept electrons from the reduced trypanothione and donate their electrons to other proteins, and these proteins reduce toxic molecules, neutralize reactive oxygen, or nitrogen species; and help parasites to cope with oxidative stress. Thus, a better understanding of the role of these molecules in drug resistance and redox homeostasis will help to target metabolic pathway proteins to combat Leishmaniasis and trypanosomiases.

Polyamine Metabolism in Leishmania Parasites: A Promising Therapeutic Target

Parasites of the genus Leishmania cause a variety of devastating and often fatal diseases in humans and domestic animals worldwide. The need for new therapeutic strategies is urgent because no vaccine is available, and treatment options are limited due to a lack of specificity and the emergence of drug resistance. Polyamines are metabolites that play a central role in rapidly proliferating cells, and recent studies have highlighted their critical nature in Leishmania. Numerous studies using a variety of inhibitors as well as gene deletion mutants have elucidated the pathway and routes of transport, revealing unique aspects of polyamine metabolism in Leishmania parasites. These studies have also shed light on the significance of polyamines for parasite proliferation, infectivity, and host-parasite interactions. This comprehensive review article focuses on the main polyamine biosynthetic enzymes: ornithine decarboxylase, S-adenosylmethionine decarboxylase, and spermidine synthase, and it emphasizes recent discoveries that advance these enzymes as potential therapeutic targets against Leishmania parasites.

Insights of antiparasitic activity of sodium diethyldithiocarbamate against different strains of Trypanosoma cruzi

Chagas disease is caused by Trypanosoma cruzi and affects thousands of people. Drugs currently used in therapy are toxic and have therapeutic limitations. In addition, the genetic diversity of T. cruzi represents an important variable and challenge in treatment. Sodium diethyldithiocarbamate (DETC) is a compound with pharmacological versatility acting as metal chelators and ROS generation. Thus, the objective was to characterize the antiparasitic action of DETC against different strains and forms of T. cruzi and their mechanism. The different strains of T. cruzi were grown in LIT medium. To evaluate the antiparasitic activity of DETC, epimastigote and trypomastigote forms of T. cruzi were used by resazurin reduction methods and by counting. Different response patterns were obtained between the strains and an IC₅₀ of DETC ranging from 9.44 ± 3,181 to 60.49 ± 7.62 µM. Cell cytotoxicity against 3T3 and RAW cell lines and evaluated by MTT, demonstrated that DETC in high concentration (2222.00 µM) presents low toxicity. Yet, DETC causes mitochondrial damage in T. cruzi, as well as disruption in parasite membrane. DETC has antiparasitic activity against different genotypes and forms of T. cruzi, therefore, representing a promising molecule as a drug for the treatment of Chagas disease.

Histone deacetylases inhibitors as new potential drugs against Leishmania braziliensis, the main causative agent of new world tegumentary leishmaniasis

The protozoan parasite Leishmania braziliensis is a major causative agent of the neglected tropical diseases Cutaneous and Mucocutaneous Leishmaniases in the New World. There are no vaccines to prevent the infection and the treatment relies on few drugs that often display high toxicity and costs. Thus, chemotherapeutic alternatives are required. Histone Deacetylases (HDACs) are epigenetic enzymes involved in the control of chromatin structure. In this work, we tested an in-house library of 78 hydroxamic acid derivatives as putative inhibitors of L. braziliensis HDACs (HDACi). The compounds were evaluated in relation to the toxicity to the host cell macrophage and to the leishmanicidal effect against L. braziliensis during in vitro infection. Eight HDACi showed significant leishmanicidal effects and the top 5 compounds showed effective concentrations (EC₅₀) in the range of 4.38 to 10.21 μM and selectivity indexes (SI) from of 6 to 21.7. Analyses by Transmission Electron Microscopy (TEM) indicated induction of apoptotic cell death of L. braziliensis amastigotes with a necrotic phenotype. An altered chromatin condensation pattern and cellular disorganization of intracellular amastigotes was also observed. A tight connection between the mitochondrion and nuclear protrusions, presumably of endoplasmic reticulum origin, was found in parasites but not in the host cell. In flow cytometry (FC) analyses, HDACi promoted parasite cell cycle arrest in the G2-M phase and no changes were found in macrophages. In addition, the direct effect of HDACi against the promastigotes showed apoptosis as the main mechanism of cell death. The FC results corroborate the TEM analyses indicating that the HDACi lead to changes in the cell cycle and induction of apoptosis of L. braziliensis. The production of nitric oxide by the infected macrophages was not altered after treatment with the top 5 compounds. Taken together, our results evidenced new HDACi as promising agents for the development of new treatments for American Tegumentary Leishmaniasis caused by L. braziliensis.

Amino Acid and Polyamine Membrane Transporters in Trypanosoma cruzi: Biological Function and Evaluation as Drug Targets

Amino acids and polyamines are involved in relevant processes for the parasite Trypanosoma cruzi, like protein synthesis, stress resistance, life cycle progression, infection establishment and redox balance, among others. In addition to the biosynthetic routes of amino acids, T. cruzi possesses transport systems that allow the active uptake from the extracellular medium; and in the case of polyamines, the uptake is the unique way to obtain these compounds. The TcAAAP protein family is absent in mammals and its members are responsible for amino acid and derivative uptake, thus the TcAAAP permeases are not only interesting and promising therapeutic targets but could also be used to direct the entry of toxic compounds into the parasite. Although there is a treatment available for Chagas disease, its limited efficacy in the chronic stage of the disease, as well as the side effects reported, highlight the urgent need to develop new therapies. Discovery of new drugs is a slow and cost-consuming process, and even during clinical trials the drugs can fail. In this context, drug repositioning is an interesting and recommended strategy by the World Health Organization since costs and time are significantly reduced. In this article, amino acids and polyamines transport and their potential as therapeutic targets will be revised, including examples of synthetic drugs and drug repurposing.

Effects of a novel β-lapachone derivative on Trypanosoma cruzi: Parasite death involving apoptosis, autophagy and necrosis

Natural products comprise valuable sources for new antiparasitic drugs. Here we tested the effects of a novel β-lapachone derivative on Trypanosoma cruzi parasite survival and proliferation and used microscopy and cytometry techniques to approach the mechanism(s) underlying parasite death. The selectivity index determination indicate that the compound trypanocidal activity was over ten-fold more cytotoxic to epimastigotes than to macrophages or splenocytes. Scanning electron microscopy analysis revealed that the R72 β-lapachone derivative affected the T. cruzi morphology and surface topography. General plasma membrane waving and blebbing particularly on the cytostome region were observed in the R72-treated parasites. Transmission electron microscopy observations confirmed the surface damage at the cytostome opening vicinity. We also observed ultrastructural evidence of the autophagic mechanism termed macroautophagy. Some of the autophagosomes involved large portions of the parasite cytoplasm and their fusion/confluence may lead to necrotic parasite death. The remarkably enhanced frequency of autophagy triggering was confirmed by quantitating monodansylcadaverine labeling. Some cells displayed evidence of chromatin pycnosis and nuclear fragmentation were detected. This latter phenomenon was also indicated by DAPI staining of R72-treated cells. The apoptotis induction was suggested to take place in circa one-third of the parasites assessed by annexin V labeling measured by flow cytometry. TUNEL staining corroborated the apoptosis induction. Propidium iodide labeling indicate that at least 10% of the R72-treated parasites suffered necrosis within 24 h. The present data indicate that the β-lapachone derivative R72 selectively triggers T. cruzi cell death, involving both apoptosis and autophagy-induced necrosis.

Discovery of novel polyamine analogs with anti-protozoal activity by computer guided drug repositioning

Chagas disease is a parasitic infection caused by the protozoa Trypanosoma cruzi that affects about 6 million people in Latin America. Despite its sanitary importance, there are currently only two drugs available for treatment: benznidazole and nifurtimox, both exhibiting serious adverse effects and limited efficacy in the chronic stage of the disease. Polyamines are ubiquitous to all living organisms where they participate in multiple basic functions such as biosynthesis of nucleic acids and proteins, proliferation and cell differentiation. T. cruzi is auxotroph for polyamines, which are taken up from the extracellular medium by efficient transporters and, to a large extent, incorporated into trypanothione (bis-glutathionylspermidine), the major redox cosubstrate of trypanosomatids. From a 268-compound database containing polyamine analogs with and without inhibitory effect on T. cruzi we have inferred classificatory models that were later applied in a virtual screening campaign to identify anti-trypanosomal compounds among drugs already used for other therapeutic indications (i.e. computer-guided drug repositioning) compiled in the DrugBank and Sweetlead databases. Five of the candidates identified with this strategy were evaluated in cellular models from different pathogenic trypanosomatids (T. cruzi wt, T. cruzi PAT12, T. brucei and Leishmania infantum), and in vitro models of aminoacid/polyamine transport assays and trypanothione synthetase inhibition assay. Triclabendazole, sertaconazole and paroxetine displayed inhibitory effects on the proliferation of T. cruzi (epimastigotes) and the uptake of putrescine by the parasite. They also interfered with the uptake of others aminoacids and the proliferation of infective T. brucei and L. infantum (promastigotes). Trypanothione synthetase was ruled out as molecular target for the anti-parasitic activity of these compounds.

Enhancement of the antibiofilm activity of amphotericin B by polyamine biosynthesis inhibitors

The aim of this study was to investigate the effect of polyamine biosynthesis inhibitors on the activity of amphotericin B (AmB) against Candida albicans biofilms and to clarify the underlying mechanisms. The antibiofilm activity of AmB was significantly enhanced when used in combination with the polyamine biosynthesis inhibitors 1,4-diamino-2-butanone (DAB) and α-difluoromethylornithine (DFMO). Further study showed that DAB and DFMO also enhanced the antibiofilm activity of several other antifungal agents. Moreover, the combination of AmB and polyamine biosynthesis inhibitors resulted in an increase in intracellular levels of reactive oxygen species. In addition, caspase activity and transcription of the caspase-encoding gene CaMCA1 were greatly increased upon combined treatment with polyamine biosynthesis inhibitors and AmB. Consistently, the biofilm formed by a Δcamca1 mutant exhibited greater viability and lower caspase activity than that of the wild-type strain upon combined treatment. These data provide useful information for the development of new strategies to enhance the antibiofilm activities of antifungal agents.

Cytotoxicity of 1,4-diamino-2-butanone, a putrescine analogue, to RKO cells: mechanism and redox imbalance

α-Aminocarbonyl metabolites (e.g., 5-aminolevulinic acid and aminoacetone) and the wide spectrum microbicide 1,4-diamino-2-butanone (DAB) have been shown to exhibit pro-oxidant properties. In vitro, these compounds undergo phosphate-catalyzed enolization at physiological pH and subsequent superoxide radical-propagated aerobic oxidation, yielding a reactive α-oxoaldehyde and H2O2. DAB cytotoxicity to pathogenic microorganisms has been attributed to the inhibition of polyamine biosynthesis. However, the role played in cell death by reactive DAB oxidation products is still poorly understood. This work aims to clarify the mechanism of DAB-promoted pro-oxidant action on mammalian cells. DAB (0.05-10 mM) treatment of RKO cells derived from human colon carcinoma led to a decrease in cell viability (IC50 ca. 0.3 mM DAB, 24 h incubation). Pre-addition of either catalase (5 μM) or aminoguanidine (20 mM) was observed to partially inhibit the toxic effects of DAB to the cells, while N-acetyl-L-cysteine (NAC, 5 mM) or reduced glutathione (GSH, 5 mM) provided almost complete protection against DAB. Changes in redox balance and stress response pathways were indicated by the increased expression of HO-1, NQO1 and xCT. Moreover, the observation of caspase 3 and PARP cleavage products is consistent with DAB-triggered apoptosis in RKO cells, which was corroborated by the partial protection afforded by the pan-caspase inhibitor z-VAD-FMK. Finally, DAB treatment disrupted the cell cycle in response to increased p53 and activation of ATM. Altogether, these data support the hypothesis that DAB exerts cytotoxicity via a mechanism involving not only polyamine biosynthesis but also by DAB oxidation products.

Leishmanicidal activity of Cecropia pachystachya flavonoids: arginase inhibition and altered mitochondrial DNA arrangement

The plant Cecropia pachystachya Trécul is widely used in Brazilian ethnomedicine to treat hypertension, asthma, and diabetes. Arginase is an enzyme with levels that are elevated in these disorders, and it is central to Leishmania polyamine biosynthesis. The aims of this study were to evaluate antileishmanial activity and inhibition of the arginase enzyme by C. pachystachya extracts, and to study changes in cellular organization using electron microscopy. The ethanol extract of C. pachystachya was tested on Leishmania (Leishmania) amazonensis promastigote survival/proliferation and arginase activity in vitro. Qualitative ultrastructural analysis was also used to observe changes in cell organization. The major bioactive molecules of the ethanol extract were characterized using liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). The ethyl acetate fraction of the ethanol extract diminished promastigote axenic growth/survival, inhibited arginase activity, and altered a mitochondrial kinetoplast DNA (K-DNA) array. The bioactive compounds of C. pachystachya were characterized as glucoside flavonoids. Orientin (9) (luteolin-8-C-glucoside) was the main component of the methanol-soluble ethyl acetate fraction obtained from the ethanol extract and is an arginase inhibitor (IC50 15.9 μM). The ethyl acetate fraction was not cytotoxic to splenocytes at a concentration of 200 μg/mL. In conclusion, C. pachystachya contains bioactive compounds that reduce the growth of L. (L.) amazonensis promastigotes, altering mitochondrial K-DNA arrangement and inhibiting arginase.

Heme-induced ROS in Trypanosoma cruzi activates CaMKII-like that triggers epimastigote proliferation. One helpful effect of ROS

Heme is a ubiquitous molecule that has a number of physiological roles. The toxic effects of this molecule have been demonstrated in various models, based on both its pro-oxidant nature and through a detergent mechanism. It is estimated that about 10 mM of heme is released during blood digestion in the blood-sucking bug's midgut. The parasite Trypanosoma cruzi, the agent of Chagas' disease, proliferates in the midgut of the insect vector; however, heme metabolism in trypanosomatids remains to be elucidated. Here we provide a mechanistic explanation for the proliferative effects of heme on trypanosomatids. Heme, but not other porphyrins, induced T. cruzi proliferation, and this phenomenon was accompanied by a marked increase in reactive oxygen species (ROS) formation in epimastigotes when monitored by ROS-sensitive fluorescent probes. Heme-induced ROS production was time-and concentration-dependent. In addition, lipid peroxidation and the formation of 4-hydroxy-2-nonenal (4-HNE) adducts with parasite proteins were increased in epimastigotes in the presence of heme. Conversely, the antioxidants urate and GSH reversed the heme-induced ROS. Urate also decreased parasite proliferation. Among several protein kinase inhibitors tested only specific inhibitors of CaMKII, KN93 and Myr-AIP, were able to abolish heme-induced ROS formation in epimastigotes leading to parasite growth impairment. Taken together, these data provide new insight into T. cruzi- insect vector interactions: heme, a molecule from the blood digestion, triggers epimastigote proliferation through a redox-sensitive signalling mechanism.

Polyamine homoeostasis as a drug target in pathogenic protozoa: peculiarities and possibilities

New drugs are urgently needed for the treatment of tropical and subtropical parasitic diseases, such as African sleeping sickness, Chagas' disease, leishmaniasis and malaria. Enzymes in polyamine biosynthesis and thiol metabolism, as well as polyamine transporters, are potential drug targets within these organisms. In the present review, the current knowledge of unique properties of polyamine metabolism in these parasites is outlined. These properties include prozyme regulation of AdoMetDC (S-adenosylmethionine decarboxylase) activity in trypanosomatids, co-expression of ODC (ornithine decarboxylase) and AdoMetDC activities in a single protein in plasmodia, and formation of trypanothione, a unique compound linking polyamine and thiol metabolism in trypanosomatids. Particularly interesting features within polyamine metabolism in these parasites are highlighted for their potential in selective therapeutic strategies.

1,4-Diamino-2-butanone, a wide-spectrum microbicide, yields reactive species by metal-catalyzed oxidation

The α-aminoketone 1,4-diamino-2-butanone (DAB), a putrescine analogue, is highly toxic to various microorganisms, including Trypanosoma cruzi. However, little is known about the molecular mechanisms underlying DAB's cytotoxic properties. We report here that DAB (pK(a) 7.5 and 9.5) undergoes aerobic oxidation in phosphate buffer, pH 7.4, at 37°C, catalyzed by Fe(II) and Cu(II) ions yielding NH(4)(+) ion, H(2)O(2), and 4-amino-2-oxobutanal (oxoDAB). OxoDAB, like methylglyoxal and other α-oxoaldehydes, is expected to cause protein aggregation and nucleobase lesions. Propagation of DAB oxidation by superoxide radical was confirmed by the inhibitory effect of added SOD (50 U ml-1) and stimulatory effect of xanthine/xanthine oxidase, a source of superoxide radical. EPR spin trapping studies with 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) revealed an adduct attributable to DMPO-HO(•), and those with α-(4-pyridyl-1-oxide)-N-tert-butylnitrone or 3,5-dibromo-4-nitrosobenzenesulfonic acid, a six-line adduct assignable to a DAB(•) resonant enoyl radical adduct. Added horse spleen ferritin (HoSF) and bovine apo-transferrin underwent oxidative changes in tryptophan residues in the presence of 1.0-10 mM DAB. Iron release from HoSF was observed as well. Assays performed with fluorescein-encapsulated liposomes of cardiolipin and phosphatidylcholine (20:80) incubated with DAB resulted in extensive lipid peroxidation and consequent vesicle permeabilization. DAB (0-10 mM) administration to cultured LLC-MK2 epithelial cells caused a decline in cell viability, which was inhibited by preaddition of either catalase (4.5 μM) or aminoguanidine (25 mM). Our findings support the hypothesis that DAB toxicity to several pathogenic microorganisms previously described may involve not only reported inhibition of polyamine metabolism but also DAB pro-oxidant activity.

DETC induces Leishmania parasite killing in human in vitro and murine in vivo models: a promising therapeutic alternative in Leishmaniasis

Background

Chemotherapy remains the primary tool for treatment and control of human leishmaniasis. However, currently available drugs present serious problems regarding side-effects, variable efficacy, and cost. Affordable and less toxic drugs are urgently needed for leishmaniasis.

Methodology/Principal Findings

We demonstrate, by microscopy and viability assays, that superoxide dismutase inhibitor diethyldithiocarbamate (DETC) dose-dependently induces parasite killing (p<0.001) and is able to “sterilize” Leishmania amazonensis infection at 2 mM in human macrophages in vitro. We also show that DETC-induced superoxide production (p<0.001) and parasite destruction (p<0.05) were reverted by the addition of the antioxidant N-acetylcysteine, indicating that DETC-induced killing occurs through oxidative damage. Furthermore, ultrastructural analysis by electron microscopy demonstrates a rapid and highly selective destruction of amastigotes in the phagosome upon DETC treatment, without any apparent damage to the host cell, including its mitochondria. In addition, DETC significantly induced parasite killing in Leishmania promastigotes in axenic culture. In murine macrophages infected with Leishmania braziliensis, DETC significantly induced in vitro superoxide production (p = 0.0049) and parasite killing (p = 0.0043). In vivo treatment with DETC in BALB/C mice infected with Leishmania braziliensis caused a significant decrease in lesion size (p<0.0001), paralleled by a 100-fold decrease (p = 0.0087) in parasite burden.

Conclusions/Significance

Due to its strong leishmanicidal effect in human macrophages in vitro, its in vivo effectiveness in a murine model, and its previously demonstrated in vivo safety profile in HIV treatment, DETC treatment might be considered as a valuable therapeutic option in human leishmaniasis, including HIV/Leishmania co-infection.

In vitro anti-trypanosomal activity of elatol isolated from red seaweed Laurencia dendroidea

SUMMARY

Chagas' disease is a debilitating but comparatively neglected illness that affects about 15 million people. There is an urgent need to develop new, more effective, and less-toxic compounds. In this study, we assessed the in vitro anti-trypanosomal activity of the sesquiterpene elatol from the Brazilian red seaweed Laurencia dendroidea. We used electron microscopy to evaluate the effect of elatol on the morphology and ultrastructure of the parasite. Elatol showed a dose-dependent effect against the epimastigote, trypomastigote, and amastigote forms, with IC50 values of 45.4, 1.38, and 1.01 microm, respectively. Observation of treated intracellular amastigotes by light microscopy demonstrated a total elimination of the infection at a dose of 3.0 microm. In addition, the compound did not affect the red blood cells, and the CC50 value for LLCMK2 cells was 27.0 microm. Transmission and scanning electron micrographs showed aberrant-shaped cells and breaks in the plasma membrane, prominent swollen mitochondria, and extensive formation of cytoplasmic vacuoles in all the forms. This is the first report of the anti-trypanosomal effect of the sesquiterpene elatol.

In vitro and in vivo activities of 1,3,4-thiadiazole-2-arylhydrazone derivatives of megazol against Trypanosoma cruzi

From a series of 1,3,4-thiadiazole-2-arylhydrazone derivatives of megazol screened in vitro against Trypanosoma cruzi, eight (S1 to S8) were selected for in vivo screening by single-dose oral administration (200 mg/kg of body weight) to infected mice at 5 days postinfection (dpi). Based on significant decreases in both parasitemia levels and mortality rates, S2 and S3 were selected for further assays. Despite having no in vivo effect, S1 was included since it was 2-fold more potent against trypomastigotes than megazol in vitro. Trypomastigotes treated with S1, S2, or S3 showed alterations of the flagellar structure and of the nuclear envelope. When assayed on intracellular amastigotes, the selectivity index (SI) for macrophages was in the range of >27 to >63 and for cardiac cells was >32 for S1 and >48 for megazol. In noninfected mice, S1 did not alter the levels of glutamic oxalacetic transaminase (GOT), glutamate pyruvate transaminase (GPT), or urea. S2 led to an increase in GOT, S3 to increases in GOT and GPT, and megazol to an increase in GOT. Infected mice were treated with each derivative at 50 and 100 mg/kg from dpi 6 to 15: S1 did not interfere with the course of infection or reduce the number of inflammatory foci in the cardiac tissue, S2 led to a significant decrease of parasitemia, and S3 decreased mortality. There was no direct correlation between the in vitro effect on trypomastigotes and amastigotes and the results of the treatment in experimental models, as S1 showed a high potency in vitro while, in two different schemes of in vivo treatment, no decrease of parasitemia or mortality was observed.

The effects on Trypanosoma cruzi of novel synthetic naphthoquinones are mediated by mitochondrial dysfunction

Despite ongoing efforts, the current treatment for Chagas disease is still unsatisfactory, mainly because of the severe side effects and variable efficacy of the available nitroheterocycles. Our group has been assaying natural quinones isolated from Brazilian flora, and their derivatives, as alternative chemotherapeutic agents against Trypanosoma cruzi. From C-allyl lawsone three naphthofuranquinones were synthesized, which were active against trypomastigotes and epimastigotes. Here, we further investigated the activity and the mechanisms of action of these quinones. They exhibited powerful effects on intracellular amastigotes, presenting low toxicity to the host cells. Ultrastructural analyses of treated epimastigotes and trypomastigotes indicated a potent effect of the three naphthofuranquinones on the parasite mitochondrion, which appeared drastically swollen and with a washed-out matrix profile. Fluorescence-activated cell sorting analysis of rhodamine 123-stained T. cruzi showed that the three naphthofuranquinones caused a potent dose-dependent collapse of the mitochondrial membrane potential, especially in the epimastigote form. Naphthofuranquinones also decreased specifically mitochondrial complex I-III activity in both epimastigotes and trypomastigotes, parallel to a reduction in succinate-induced oxygen consumption. Mitochondrial hydrogen peroxide formation was also increased in epimastigotes after treatment with the naphthofuranquinones. Our results indicate that the trypanocidal action of the naphthofuranquinones is associated with mitochondrial dysfunction, leading to increased reactive oxygen species generation and parasite death.

Spermine isolated and identified as the major trypanocidal compound from the snake venom of Eristocophis macmahoni causes autophagy in Trypanosoma brucei

The snake venom from the leaf-nosed viper Eristocophis macmahoni was analyzed regarding its toxic effects on the bloodstream form of Trypanosoma brucei. A considerable trypanocidal effect was measured with an IC5 value of 186 ng/ml in bloodstream form parasites. Following several high performance liquid chromatography (HPLC) separation steps, the major trypanocidal activity was assigned to a single fraction by in vitro toxicity assays. Analysis by off-line ESI-MS(n) revealed an m/z value of 202.2 for the precursor ion and fragment ions of m/z=129.1 (MS2) and 112.1 (MS3), respectively, clearly corresponding to the molecular mass and the fragmentation pattern of the polyamine spermine. Quantification of spermine within the viper venom using an on-line hydrophilic interaction chromatography (HILIC) ESI-MS method revealed that this compound constituted approximately 1% of the dry venom mass. The polyamine oxidase activity in the fetal calf serum used for cultivation was responsible for a trypanocidal effect of pure spermine in the low micromolar range, whereas the antitrypanosomal activity of crude snake venom was virtually independent from serum, suggesting the oxidation of spermine by intrinsic venom components. Using fetal calf serum, spermine was shown to induce autophagy in the parasites using transmission electron microscopy (TEM).